Project Summary/Abstract Metabolomics is a relatively novel Molecular Biological Tool (MBT), which employs highly sensitive instrumentation to obtain a measure of all small organic molecules present in a biological sample. Contemporary MBTs rely on quantitative PCR and measure the presence and abundance of keystone bacteria (e.g., Dehalococcoides) involved in the detoxification of priority contaminants such as chlorinated ethenes; however, the current tools fall short of informing about actual in situ dechlorination activity. Metabolomics measures small molecules that directly relate to active metabolism, and provides key insights into microbial community function and health. Chlorinated ethenes are among the most common contaminants impacting Superfund sites. Detoxification can be achieved by organohalide-respiring bacteria (e.g., Dehalococcoides) via stepwise reductive dechlorination to environmentally benign ethene; however, the degradation process often stalls at the toxic and carcinogenic intermediates cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). MBTs applied in contemporary monitoring regimes cannot predict the occurrence of stalls, and costly remediation strategy changes are required. Laboratory experiments demonstrated that metabolomics distinguishes healthy microbiomes from ?sick? microbiomes and predicts degradation stalls or when ethene formation occurs. An MBT with these capabilities would greatly reduce overall project costs and management time, streamline the implementation of the most promising remedy, contribute to early site closures, and thus be a valuable asset to the remediation industry with tangible benefits to the U.S. tax payer. The proposed study will demonstrate the value and utility of the metabolomics approach as a prognostic and diagnostic monitoring tool for the remediation industry, and develop a path towards commercialization of this MBT.